This invention relates generally to the flowmeter art, and more particularly concerns apparatus which measure the rate of a flowing fluid.
Flowmeters producing electrical signals representative of the mass flow rate of a fluid, such as fuel or gas, are well known. Similarly, flowmeters producing electrical signals representative of the volume flow rate of a fluid are also well known. One type of mass flowmeter includes a positively driven central shaft, a rotating drum connected to the shaft, on which drum is positioned a plurality of spaced magnets, and an impeller assembly having numerous openings positioned therein, permitting fluid to flow therethrough, the impeller being connected to the drum shaft by a spring. In operation, the positively driven shaft continuously rotates the drum which is spring coupled to the impeller assembly. The greater the fluid flow rate, the greater the quantity of fluid to which the impeller must impart angular momentum, and the greater the angular deflection of the coupling spring.
The magnets located on the periphery of both the drum and the impeller indicate the degree of their respective deflections by inducing pulse energy into a pair of stationary pickup coils positioned adjacent the path of magnets on the rotating drum and the deflected impeller. The time difference between successive pulses from the drum pickup coil and the impeller pickup coil, referred to as .DELTA.t, is representative of the mass flow rate of the fluid. The mass flow rate is in most instances the most important information concerning flow rate of a fluid. The mass flow rate of fuel, for instance, is monitored in engine testing procedures to provide an indication of engine condition, and in actual engine use to provide information concerning the rate at which fuel is being used, or the quantity of fuel remaining.
Prior art mass flowmeters, however, are relatively slow in responding to transient changes in flow and provide no information as to density or volumetric flow rate. Since mass is equal to volume times density, sudden changes in either the volume (i.e., speed of the fluid) or the density of the fluid should quickly affect the actual mass flow as well. However, mass flowmeters are slow in responding to changes in flow because a significant time constant is inroduced by the circuitry converting the .DELTA.t pulses into a corresponding DC signal for operation of the indicating circuitry, as well as by the natural resonant frequency of the spring connecting the drum and the impeller.
Accordingly, it is a general object of the present invention to provide a flowmeter which overcomes the disadvantages of prior art mass flowmeters discussed above.
It is another object of the present invention to provide a flowmeter which provides an adjusted mass flow output signal representative of the mass flow rate, which reflects changes in the volume flow of fluid substantially as they occur.
It is a further object of the present invention to provide such a flowmeter which uses electrical signals representative of mass flow and volumetric flow to generate the adjusted mass flow output signal.
It is yet another object of the present invention to provide such a flowmeter which also generates such electrical signals representative of mass flow and volume flow in a single flowmeter unit.
It is a still further object of the present invention to provide such a flowmeter which may be utilized with existing flowmeters providing electrical signals representative of mass and volumetric flow signal information.